Transcript
United States Patent [191
[11] Patent Number:
Franke
[45]
[541 ANTENNA WIIH ENHAN CED GAIN [75]
Inventor:
Jan. 8, 1991
1201200 2/1935 Canada . 0121641
Iii-Systems, 111% Dallas, TeX-
9/1979
Japan ................................. .. 343/850
2065376 6/1981 United Kingdom .
[21] Appl. No.: 273,562
Primary Examiner-Rolf Hille
_
Assistant Examiner-Peter Toby Brown
[22] Flled: [51] [52]
Date of Patent:
FOREIGN PATENT DOCUMENTS
Ernest A. Franke, Largo, Fla.
_
[73] Asslsnw
4,983,988
Nov. 21, 1988
Attorney, Agent, or Firm-Harold E. Meier
Int. c1.5 ........................................... .. HOIQ 21/00 US. CL ................................... .. 343/853; 343/836
[58] Field ofSearch .............. .. 343/796, 797, 799-814,
[57] ABSTRACT Represent invention will yield enhanced gain over a conventional antenna system by taking advantage of
343/815-8202 834’ 835’ 836’ 85o’ 351’ 8-53
combining directional antennae. In one embodiment,
. References cued U-S- PATENT DOCUMENTS
[56]
the invention utilizes four 10 dB dipole, vertically-pola rized, omni-directional antennae having a re?ector added to each one to limit the horizontal beamwidth to
2,867,804 1/1959 Gihring
343/853
99' and inclfease ‘he 8811112 1,6 dB- The vertical beam‘
3,064,212 3,545,001 4,101,836 4,101,901 4,103,304
333 A07 343/817 325/302 343/853 343/853 352/370
width remains at 7°. By utilizing four of these antennae and utilizing power combining hybrids to connect each of the two opposed antennae together, excess gain over a 10 dB omni-directional system will be obtained. The effective antenna gain is equal to the directional antenna gain minus the omni-directional antenna gain minus the
'
’
11/1962 12/1970 7/1978 7/1978 7/ 1978 5/ 10/
Alford Giller ..... .. Craig et al. . Kommrusch Bumham et a1 Osborn """""" " .
5/51
4,213,132
7/1980 Davidson
4,814,777
3/1989 Mouser .............................. .. 343/799
4,317,229 2/1982 Craig et a1 4,446,465 5/1984 Donovan 4,519,096 5/1985 Ccmy, Jr
343/814
455/277 343/797 455/137
hybrid loss. Thus, the vertical beamwidth and physical h . ht fth
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omni-directional antennae with the use of reflectors. By decreasing the horizontal angle of coverage of the om
ANTENNA WITH ENHANCED GAIN
ni-directional antenna, additional gain is achieved with out sacri?cing vertical beamwidth. Thus, at least four 16 dBd vertically L polarized antennae are formed by taking 10 dBd omni-directional antennae and adding
TECHNICAL FIELD The present invention relates generally to antenna systems and, in particular, to combined directional an tennae having increased effective received signal power
re?ectors to limit the horizontal beamwidth to 90°. The vertical beamwidth remains at 7“. Power combining limited physical height. 10 hybrids connect each of the two opposed directional BACKGROUND OF THE INVENTION antennae. The output signal from the two hybrids is coupled to a diversity receiver where the amplitude and Omni-directional antennae are in wide use in commu phase of the signals are adjusted and combined in a nication systems. In such systems, there is an attempt to constructive manner. maximize antenna gain in order to maximize the carrier The invention may combine N such directional an to-noise ratio and carrier-to-interference ratio. One method of maximizing omni-directional antenna gain is tennae, where N is an even number éZ, with each two to stack dipoles in a collinear manner. There are, how opposing antenna outputs being coupled to a passive while maintaining a wide vertical beamwidth and a
ever, two limitations which must be considered when
power combining hybrid. The output of each of the hybrids is then coupled to the diversity receiver. Thus, the invention provides an improved system
maximizing antenna gain by stacking dipoles in a collin ear manner.
The ?rst limitation is created by physical problems
having enhanced antenna gain with the use of at least four directional antennae covering a 360" horizontal beamwidth sector and a ?xed vertical beamwidth sector and where each individual antenna is arranged to cover
associated with the antenna. It is well known that the power gain of an omni-directional, collinear antenna
varies directly with the length of the radiator. Thus, the longer the antenna, the greater the gain. However, simply increasing the length of the antenna to achieve the gain creates other problems. The Federal Communi cations Commission Rules require aircraft warning
no more than a 90° beamwidth sector. A power com
biner (hybrid) is coupled to each opposed pair of anten nae for combining the signals from the opposed anten nae and a single channel diversity receiver is coupled to
lighting on any antenna, itself, that extends more than twenty feet above the top of a tower, building or water tower. Thus, to achieve greater gain, decoupling net
the hybrid combiners for optimally adjusting the phase and amplitude of each signal and combining the signals. Each of the directional antennae comprises an omni directional antenna and a reflector associated with each antenna to limit the horizontal beamwidth to no more
works would be required as well as a side ladder for
changing the required lights. The additional length, then, creates both electrical and mechanical problems which are not easily solved without greater expenses
than 90°. In the general embodiment of the invention, at least N directional antennae covering 360° horizontal beam width sector and having a ?xed vertical beamwidth
being required. As the length of the antenna is in creased, the physical strength of the antenna must be increased to account for the increased loading under _ wind loading conditions due to the longer lever arm.
sector are constructed such that each individual antenna is arranged to cover no more than a 360°/N beamwidth
The second limitation on achieving higher gain by stacking dipoles is the compression of the vertical beam
sector where N=an even number 22. Thus, N=2, 4, 6, width as the antenna is increased in length and the gain 45 8 and the like. is increased. The beamwidth decreases by a factor of 2 Further, the equipment arrangement as disclosed to achieve each increase in antenna gain of 3 dB. As the herein, has a single channel (frequency) for each re beam narrows the criticality of mounting and of main ceiver. To accommodate multiple channels, a pream
taining the exact perpendicular position of the antenna,
even under wind loading, becomes very important. For a 10 dBd gain antenna, a movement of as slight as 3?
under high wind conditions, would cause a loss in signal level of 3 dB. It is apparent that such a higher gain antenna must be built more rugged, thus requiring heavier material to be used, in order to form more sub stantial towers for maintaining the antenna in a ?xed position at all times. Further, as the beamwidth nar rows, the dead zone or cone of silence beneath the antenna increases. This produces more dead spots. Fur ther, phasing harnesses become more critical as the number of stacked elements increase.
50
pli?er/power splitter (multi-coupler) is needed for each signal lead from each combining hybrid feeding each diversity receiver. SUMMARY OF THE INVENTION Thus, in accordance with the present invention, a system having enhanced antenna gain comprises at least N directional antennae covering a 360° horizontal beamwidth sector, and having a ?xed vertical beam width sector, each individual antenna arranged to cover no more than a 360°/N horizontal beamwidth sector where N=an even number 52, a power hybrid com
biner coupled to each opposed pair of antenna for com The present invention overcomes disadvantages of bining the signals from the opposed antennae and a the prior art by allowing antenna gain to be increased 65
without increasing the antenna length (height) and without compressing the vertical beamwidth. This is accomplished by limiting the horizontal beamwidth of
single channel diversity receiver coupled to the output of the hybrid combiners for adjusting the phase and amplitude of each signal and combining the signals.
3
4,983,988
4
The invention also relates to a method for enhancing
tween a dipole and an isotropic antenna. The result of
antenna gain comprising the steps of covering a 360°
this relationship as expressed by equation (1) is shown
horizontal beamwidth sector having a ?xed vertical beamwidth with at least N directional antennae, each
graphically in FIG. 1 and applies generally to commer cial omni-directional antennae. The theoretical relation
individual antenna covering no more than a 360°/N horizontal beamwidth sector where N=an even num
ship graphed in FIG. 1 of the omni-directional gain versus the relative antenna length compares very closely to actual tests. It can be seen in FIG. 1 that
ber 22, coupling a power hybrid combiner to each
opposed pair of antennae for combining the signals for the opposed antennae, and coupling a single channel diversity receiver to the hybrid combiners for adjusting the phase and amplitude of each signal and combining the signals.
omni-directional antenna gain does increase logarithmi O cally with an increase in the relative antenna length.
However, increasing the length of the antenna, itself,
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph illustrating the relationship of the antenna gain to relative antenna length and applies gen erally to commercial omni-directional antennae; FIG. 2A is a graph illustrating the vertical pro?le of 20 stacked vertical dipoles showing a reduced vertical
beamwidth, 0,; FIG. 2B represents the vertical pro?le of a dipole
element illustrating the vertical beamwidth, 0,; FIG. 3 is a graph illustrating omni-directional an tenna gain as a function of vertical beamwidth as calcu
lated theoretically; FIG. 4 is a graph illustrating the directional gain of an omni-directional antenna as a function of the product of
the vertical and horizontal beamwidths; FIG. 5 is a schematic representation of the present invention employing four omni-directional antennae and associated reflectors and power combining hybrids
creates further problems. First, the Federal Communi cations Commission Regulations state that if the an tenna, itself, extends more than twenty foot above the top of a tower, building or water tower, it will require
aircraft warning lighting. This would involve decou pling networks and a side ladder for changing the lights and thus, are additional expenses that present electrical
and mechanical problems. The second limitation on achieving higher gain by stacking dipoles in a collinear manner is that decreasing values of vertical beamwidths occur with an increase in antenna length. The half-power beamwidth for an an
tenna gain of 10 dB, for example, is only 7". Omni-direc tional antenna gain is achieved by stacking dipoles at the expense of compressing the vertical beamwidth. The beamwidth decreases by a factor of 2 to achieve 30 each increase in antenna gain of 3 dB. FIG. 2A is a
graph illustrating a vertical pro?le of stacked vertical dipoles showing the reduced vertical bandwidth, 0,. As
to connect two opposing 16 dB, 90° horizontal beam
the vertical beamwidth narrows, the criticality of mounting the antenna and of maintaining the exact per
width antennae together and coupling the output of the hybrids to a single channel diversity receiver; FIG. 6 is a graph illustrating the individual patterns
more important. For the 10 dBd gain antenna, a move ment of 312" under high wind conditions will cause a loss
pendicular position, even under wind loading, becomes
of the 16 dBd directional antennae with the dotted line
in signal level of 3 dB. Thus, higher gain antennae
showing the effective omni-directional pattern achieved by a coherent co-phase combiner; and
formed in such a manner must be built in a more rugged or heavy fashion and have substantially more towers to
FIG. 7 is a schematic representation of the invention
support it. Further, as the vertical beamwidth narrows,
where six antennae are used.
the dead zone or cone of silence beneath the antenna
increases. This produces more dead spots. Finally, phas
45 DETAILED DESCRIPTION OF THE ing harnesses become more critical as the number of DRAWINGS stacked elements increase. It is apparent, therefore, that Omni-directional communication systems are well antenna gain must be increased while maintaining a known in the art and efforts are continually made to limitation on maximum antenna height and on minimum
improve their performance and maximize antenna gain.
vertical beamwidth.
A desirable result from maximizing antenna gain would be the maximizing of the resulting carrier-to-noise ratio
The theoretical gain at the center lobe of a directional antenna can be calculated if the half-power beamwidths
and carrier-to-interference ratio. It would seem obvious that to maximize omni-directional antenna gain that dipoles could be stacked in a collinear manner. How
are given by the vertical (elevation) and horizontal (azimuth) angles. The maximum gain over an isotropic radiator is calculated by dividing the area of the ellipse (or circle) of the radiation pattern at the half-power angles into the surface area of a sphere (411' square radi ans) as shown by
ever, there are two considerations which must be taken
into account by this procedure. At frequencies below 100 MHz, a physical problem is created by stacking dipoles to achieve a gain of more than 4 dB. The power gain of an omni-directional, collinear antenna, in deci bels with respect to that of a dipole, can be approxi
Gi=41T/(9H)(9v)
(2)
where G,-=the maximum gain over an isotopic radiator, 011 is the horizontal beamwidth in radians and 0,, is the cdbd=1o log (2L/M-—2. l5 (1) 65 vertical beamwidth in a plane at right angles. If the half-power beamwidths are expressed in degrees, then where L is the length of the radiator and l» is the wave length, and 2.15 is the relationship in decibels (dB) be
mated by the expression for optimal spacing,
5
4,983,988
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Consider, now, the gain at the center of the main lobe
Since a half-wave dipole has a gain of 1.64 (2.15 dB)
of a 90° horizontal beamwidth directional antenna com
over an isotropic radiator, the directional gain of an
pared with the gain of a vertically polarized omni-direc tional antenna, assuming equal vertical capture angles for both antennae. The gain difference, G, is simply
antenna at the center of the main lobe over a half-wave
dip’ole is 6,134: 10 log1()[25, 154/(9°H>< 0°,)]
(4)
G(90° directional antenna aver 0mn1')=l0 log
(360°/90°)=6.02 dB
The theoretical maximum gain has assumed that there is no radiation off the back of the antenna or in spurious side lobes. Even if the side lobes are down 10 dB from
the main lobe, the antenna gain will be incorrect only by two-tenths or three-tenths of a decimal. This also as
sumes good phase-combining by the many antenna ele ments over a reasonable bandwidth.
For the special case of a doughnut-type pattern of a
simple dipole mounted vertically to achieve omni-direc
(10)
Thus, it can be seen that by decreasing the horizontal angle of coverage of the omni-directional antenna, addi tional gain can be achieved without sacri?cing vertical beamwidth. This is clear from the above formulas where the product of the vertical and horizontal beam width determines the antenna gain as shown in FIG. 4
theoretically. This graph includes vertical antennae with 30° to 180° of horizontal beamwidth and represents all types of antennae such as Yagis, corner re?ectors,
tional coverage, the gain with reference to an isotropic 20 dipoles, stacked collinear dipoles, panels and collinears with re?ectors. The concepts set forth above are used in the present G,-=41r/(21r0v)=Z/9vrad (5) invention. In its simplest form, the invention entails the
antenna reduces to
25 use of four directional antennae and two passive power
and, expressed in degrees, this becomes 6,: 114.6/0‘,
(6)
combining hybrids. In FIG. 5, the enhanced antenna array 10 includes the four directional antennae 12, 14, 16 and 18 each of which has a corresponding added re?ector 20, 22, 24 and 26 to limit the horizontal beam
The vertical beamwidth, 6,, is determined by the half-power points, as shown in FIG. 2B. The maximum 30 width of each antenna to 90". The vertical beamwidth gain over an isotropic antenna for an omni-directional
antenna at the center of the lobe, assuming 100% effi
ciency, is more closely approximated by 6:131: 10 log10[l/sin (WV/2)]
(7)
where 0,. is the full vertical beamwidth in degrees. The more common value is the gain reduced to a half-wave
dipole as illustrated by GdBd=(GdEi— 2. 1 5)dBd
remains at 7°. The two opposing antennae 12 and 16 are coupled through conductors 28 and 30 to a 3 dB power combin 35 ing hybrid 32. In like manner, the other two opposing
antennae l4 and 18 are coupled through conductors 34 and 36 to 3 dB power combining hybrid 38. A 3 dB loss in each of the combiners 32 and 38 can be assumed because the incoming signal from a mobile in any one
antenna will not appear in the nonadjacent (back side) (8)
or
antenna. The front-to-back ratio of the antenna is typi
cally greater than 20 dB, therefore, the antenna doesn’t see anything from its backside. Thus, the excess gain 45 over a 10 dB omni system, assuming equal elevation
beamwidths, is represented by the expression
The Electronic Industry Association Standard RS
Excess Gain =Antenna Gain With Re?ection - Original A ntenna Gain —- Loss of Hybrid
329 references all gain measurements to a half-wave
dipole. To achieve this gain, no power can be spent in backward radiation or in spurious side lobes. If these
Thus, excess antenna gain, 65, is represented as
lobes are 15 dB or more below the strength of the main
65: 16.02 dBd- 10 dBd-3.0l dBd=3.0l dBd
(11)
lobe, the above formula is quite accurate. As the gain of the antenna is increased by stacking 55 The effective antenna gain is thus equal to the direc tional antenna gain, minus the omni-directional antenna dipole elements, the vertical beamwidth is decreased. gain, minus the hybrid loss. The vertical beamwidth and The flattening of the vertical beamwidth with an in physical height of the antenna have been preserved and crease in omni-directional antenna gain is illustrated the gain increased at the cost of a little antenna com theoretically in FIG. 3. A survey of commercial omni directional antennae were compared with the theoreti cal and the agreement between the theoretical and prac
plexity. The two power combining hybrids 32 and 38 feed a
diversity receiver 40. At VHF frequencies and above diversity receivers are typically used to combat multi accurately represents the relationship between the gain of an omni-directional antenna and the vertical beam 65 path effects. There are basically three types of diversity combining systems in practical use. They are selection width. As more elements are added to the stacked di
tical is very good. Thus, the graph illustrated in FIG. 3
poles, the classic doughnut-shape of the dipole flattens out to produce a disk.
diversity, maximal-ratio diversity and equal gain diver sity systems. The diversity combiner effectively adjusts
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the amplitude and phase of each signal to combine the
maintaining a wide vertical beamwidth and a limited
two signals in a constructive manner.
height.
The horizontal antenna pattern shown in FIG. 6 illus trates the individual patterns of the four 16 dBd direc tional antennae. The dotted line 42 illustrates the effec tive omni-directional pattern achieved by a coherent co-phase combiner. The net result is reduced by the hybrid power combiner 32 and 38 to 13 dBd. Theequipment arrangement shown in FIG. 5 is for a
Although the invention has been discussed, at this point, with respect to four antennae, it can be actually be used with an array. FIG. 7 discloses such an array where N=6. The enhanced antenna array 56 of FIG. 7
includes six omni-directional antennae 58, 60, 62, 64, 66 and 68. Since there are six antennae, the reflectors must be constructed so as to limit the horizontal radiation beamwidth of each antenna to 360°/ 6 or 60°. Therefore, each of the antenna 58 through 68 becomes a directional antenna which radiates in a horizontal beamwidth of
single channel (frequency) for each receiver. To accom
modate multiple channels, a preampli?er/power splitter (multi-coupler) is needed for each signal lead feeding each diversity receiver. Thus, as can be seen in FIG. 8, the hybrids 32 and 38 are identical to those illustrated in FIG. 5 and generate outputs on lines 33 and 39 to
60". Hybrid 70 receives the outputs from opposed an
preampli?er/power splitter 44 and 46, respectively.
antennae 58 and 64 on lines 78 and 80, respectively. Power combiner network 82 receives the output from opposing antennae 60 and 66 on lines 84 and 86, respec
tennae 62 and 68 on lines 72 and 74, respectively. Power
combiner hybrid 76 receives the outputs of opposing
Splitter 44 produces ?rst output on line 48 which is
coupled to diversity receiver 40 and a second output on line 50 which is coupled to a second single channel tively, and combines them. The hybrid combiners 70, 76 diversity receiver 40’. In like manner, preampli?er/ and 82 generate outputs on lines 88, 90 and 92, respec power splitter 46 generates a ?rst output on line 52 tively, which are coupled to the three branch single which is coupled to second diversity receiver 40’ and a channel diversity receiver 94. Thus, while FIG. 7 is second output on line 54 which is coupled to the ?rst 25 illustrative only, it can be seen that any number of an diversity receiver 40. Thus, two channels are shown in tennae, N, can be used in such con?guration where N is FIG. 8. However, more channels could be added by an even number 22.
coupling further outputs from the power splitters to additional single channel diversity receivers.
Thus, there has been disclosed a novel antenna sys tem and method in which antenna gain is increased
FIG. 7 illustrates the natural progression of the en hanced antenna gain concept shown for the case of six receiving antennae. The effective gain over an omni
while maintaining a limitation on maximum antenna
height and on minimum vertical beamwidth. The inven tion yields enhanced gain over conventional antenna
directional system is equal to 35
GE=[l0 log lO(N)-3.0l]dBd
(l2)
systems by taking advantage of cleverly combining directional antennae. While the simplest embodiment entails the use of four directional antennae and two
where N is the number of directional antennae and 3.01 dB is the loss in an equal-split power divider (3 dBd hybrid). For a six antenna system as shown in FIG. 7, the excess gain, GE, offered over a nominal 10 dBd
omni-directional receiver system is shown by the equa
passive power combining hybrids, the invention encom passes the use of N directional antennae and N/2 pas
sive power combining hybrids. Each hybrid connects two opposing (10+ 10 log N) dB gain, 360/N horizontal beamwidth antennae together. Each vertically polar ized antenna is formed by taking a 10 dBd omni-direc tional antenna and adding a reflector to limit the hori
tion
Gg=[l0 log (6)~3.0l]=4.77 dBd
(13) 45 zontal beamwidth to 360°/N. Where N= 6, for example,
the horizontal beamwidth is limited by the re?ector to 60° and the gain of each antenna is 17.8 dB. Where N=4, the re?ector limits the horizontal beamwidth to 50 90°, and the gain of each antenna is 16 dB. In all cases, GE=[10 log (36)-3.0l]= 12.6 dBd (14) the vertical beamwidth however remains ?xed at 7°. While the invention has been described in connection The above analysis represents an omni-directional with a preferred embodiment, it is not intended to limit antenna system. If the need for sector coverage is less, the scope of the invention to the particular form set the principal works the same. If it is desired to limit the 55 forth, but, on the contrary, it is intended to cover such coverage to a certain sector for geographical or politi alternatives, modi?cations and equivalence as may be cal reasons, the same techniques of combining can be included within the spirit and scope of the invention as If each antenna horizontal beamwidth is limited to 10°, the excess gain of a 36 antenna array is
used over that reduced coverage area.
It is also noted that in such case, the carrier-to-inter
ference ratio would improve due to the reduced proba bilistic chances that the interference (electrical noise or
another contending mobile) exists in an unused quad rant.
Once the relative angle of the mobile is extracted 65 from the receiving system, this information can be used for a switched, phase and amplitude adjusted, antenna system for increasing effective transmitted power while
de?ned in the appended claims. I claim: 1. An antenna system having enhanced gain compris
ing: at least N directional antenna combining to cover a
360° horizontal beamwidth sector and having an
established vertical beamwidth, each individual antenna including an omni-directional antenna and a reflector element to limit the horizontal beam
width of the associated omni-directional antenna to
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4,983,988
10
cover no more than a 360°/N beamwidth sector
lished vertical beamwidth, each individual antenna
where N=an even number 22;
including an omni-directional antenna and a re?ec tor element to limit the horizontal beamwidth of the associated omni-directional antenna to cover
a power combiner hybrid coupled to each opposed pair of antennae for combining the signals from the
opposed antennae; and
no more than a 360°/N beamwidth sector where
a single channel diversity receiver coupled to the
N=an even number 52;
power combiner hybrids for adjusting the phase
a power combiner hybrid coupled to each opposed pair of antennae for combining the signals from the
and amplitude of the signal from each combiner
hybrid for constructively combining the signals. 2. A system in claim 1 wherein N=4. 3. A system in claim 1 wherein N=6.
10
4. A system as in claim 1 wherein each re?ector limits the horizontal beamwidth of its associated antenna to no more than 90° without disturbing the vertical beam 15 width.
5. An antenna system having enhanced gain compris
opposed antennae; a power splitter coupled to the output of each com biner hybrid and producing at least n output signals where n=the number of frequencies to be re
ceived; 11 single channel diversity receivers individually cou - pled to one of said at least n output signals from each power splitter to accommodate one of the n
frequencies.
ing:
6. A system as in claim 5 wherein n=2.
at least N directional antennae combining to cover a
*
360° horizontal beamwidth and having an estab
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50
55
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UNITED STATES PATENT AND TRADEMARK OFFICE
CERTIFICATE OF CORRECTION PATENT NO.
I
4,983,988
DATED
I
January 8, 1991
INVENTUMS) I
Ernest A. Franke
It is certified that error appears in the above-identified patent and that said Letters Patent is hereby corrected as shown below:
.
On the title page, item [75] Inventor: "Ernest A. Franke" should be changed to ——Earnest A. Franke-—.
Column 2, line 6, delete "L". ‘Column 8, line 5, change "an array" to --an N array—-.
Signed and Sealed this
Third Day of November, 1992 Attesl: DOUGLAS B. COMER
Arresting O?cer
Acting Commissioner of Patents _and Trademarks
